In testing high density and high speed electrical devices such as LSI and VLSI circuits, high performance contact structures such as probe contactors must be used for forming an interface assembly between a test system and a device to be tested. The contact structure of the present invention is not limited to the application of testing, including burn-in testing, of semiconductor wafers and die, but is inclusive of testing and burn-in of packaged semiconductor devices, printed circuit boards and the like. The feature of the present invention can also be used in more general applications including an IC lead, IC packaging, and other electrical connections. However, for the convenience of explanation, the present invention is described mainly with reference to the semiconductor wafer testing.
In the case where semiconductor devices to be tested are in the form of a semiconductor wafer, a semiconductor test system such as an IC tester is usually accompanied with a substrate handler, such as an automatic wafer prober, to automatically test the semiconductor wafer. Such an example is shown in FIG. 1 in which a semiconductor test system has a test head 100 which is ordinarily in a separate housing and is electrically connected to the main frame of the test system with a bundle of cables. The test head 100 and the substrate handler 400 are mechanically connected with one another with the help of a manipulator 500 driven by, for example, a motor 510.
The semiconductor wafers to be tested are automatically provided to a test position of the test head 100 by the substrate handler 400. The resultant output (response) signals from IC circuits on the semiconductor wafer under test are transmitted to the semiconductor test system wherein they are compared with expected data to determine whether the IC circuits on the semiconductor wafer function correctly.
FIG. 2 shows, in more detail, a structure of the substrate handler (wafer prober) 400, the test head 100 and an interface assembly 140 when testing a semiconductor wafer. The test head 100 and the substrate handler 400 are connected with an interface assembly 140 consisting of a performance board, pogo-pin block, probe card, and other components. The performance board 120 of FIG. 2 is a printed circuit board having electric circuit connections unique to a test head's electrical footprint, coaxial cables, pogo-pins and connectors.
The test head 100 includes a large number of printed circuit boards 150 which correspond to the number of test channels or test pins. Each of the printed circuit boards has a connector 160 to receive a corresponding contact terminal 121 of the performance board 120. A "frog" ring (pogo-pin block) 130 is mounted on the performance board 120 to accurately determine the contact position relative to the substrate handler 400. The frog ring 130 has a large number of contact pins 141, such as ZIF connectors or pogo-pins, connected to contact terminals 121 on the performance board 120, through coaxial cables 124.
As shown in FIG. 2, the test head 100 is placed over the substrate handler 400 and mechanically and electrically connected to the substrate handler through the interface assembly 140. In the substrate handler 400, a semiconductor wafer 300 to be tested is mounted on a chuck 180. A probe card 170 is provided above the semiconductor wafer 300 to be tested. The probe card 170 has a large number of probe contactors or contactors (such as cantilevers or needles) 190 to contact with circuit terminals or contact targets in the IC circuit of the semiconductor wafer 300 under test.
Electrical terminals or contact receptacles of the probe card 170 are electrically connected to the contact pins 141 provided on the frog ring 130. The contact pins 141 are also connected to the contact terminals 121 of the performance board 120 with coaxial cables 124 where each contact terminal 121 is connected to the printed circuit board 150 of the test head 100. Further, the printed circuit boards 150 are connected to the semiconductor test system through the cable 110 having several hundreds of inner cables.
Under this arrangement, the probe contactors 190 contact the surface of the semiconductor wafer 300 on the chuck 180 to apply test signals to the semiconductor wafer 300 and receive the resultant output signals from the wafer 300. The resultant output signals from the semiconductor wafer 300 under test are compared with the expected data generated by the semiconductor test system to determine whether the semiconductor wafer 300 performs properly.
FIG. 3 is a bottom view of the conventional probe card 170 of FIG. 2. In this example, the probe card 170 has an epoxy ring on which a plurality of probe contactors 190 called needles or cantilevers are mounted. When the chuck 180 in the semiconductor wafer prober 400 mounting the semiconductor wafer 300 moves upward in FIG. 2, the tips of the cantilevers 190 contact the pads or bumps on the wafer 300. The ends of the cantilevers 190 are connected to wires 194 which are further connected to transmission lines (not shown) formed in the probe card 170. The transmission lines are connected to a plurality of electrodes 197 which contact the pogo pins 141 of FIG. 2.
Typically, the probe card 170 is structured by a multi-layer of polyimide substrates having ground planes, power planes, signal transmission lines on many layers. As is well known in the art, each of the signal transmission lines is designed to have a characteristic impedance such as 50 ohms by balancing the distributed parameters, i.e., dielectric constant and magnetic permeability of the polyimide, inductances and capacitances of the signal paths within the probe card 170. Thus, the signal lines are impedance matched lines establishing a high frequency transmission bandwidth to the wafer 300 for supplying currents in a steady state as well as high current peaks generated by the device's outputs switching in a transient state. For removing noise, capacitors 193 and 195 are provided on the probe card between the power and ground planes.
An equivalent circuit of the probe card 170 is shown in FIG. 4 to explain the limitation of the high frequency performance in the conventional probe card technology. As shown in FIGS. 4A and 4B, the signal transmission line on the probe card 170 extends from the electrode 197, the strip (impedance matched) line 196, the wire 194 and the needle or cantilever (contact structure) 190. Since the wire 194 and needle 190 are not impedance matched, these portions function as an inductor L in the high frequency band as shown in FIG. 4C. Because of the overall length of the wire 194 and needle 190 is around 20-30 mm, significant limitations will be resulted from the inductor when testing a high frequency performance of a device under test.
Other factors which limit the frequency bandwidth in the probe card 170 reside in the power and ground needles shown in FIGS. 4D and 4E. If the power line can provide large enough currents to the device under test, it will not seriously limit the operational bandwidth in testing the device. However, because the series connected wire 194 and needle 190 for supplying the power (FIG. 4D) as well as the series connected wire 194 and needle 190 for grounding the power and signals (FIG. 4E) are equivalent to inductors, the high speed current flow is seriously restricted.
Moreover, the capacitors 193 and 195 are provided between the power line and the ground line to secure a proper performance of the device under test by filtering out the noise or surge pulses on the power lines. The capacitors 193 have a relatively large value such as 10 .mu.F and can be disconnected from the power lines by switches if necessary. The capacitors 195 have a relatively small capacitance value such as 0.01 .mu.F and fixedly connected close to the DUT. These capacitors serve the function as high frequency decoupling on the power lines. In other words, the capacitors limit the high frequency performance of the probe contactor.
Accordingly, the most widely used probe contactors as noted above are limited to the frequency bandwidth of approximately 200 MHz which is insufficient to test recent semiconductor devices. In the industry, it is considered that the frequency bandwidth comparable to the tester's capability, which is currently on the order of 1 GHz or higher, will be necessary in the near future. Further, it is desired in the industry that a probe card is capable of handling a large number of semiconductor devices, especially memories, such as 32 or more, in a parallel fashion to increase test throughput.
In the conventional technology, the probe card and probe contactors such as shown in FIG. 3 are manually made, resulting in inconsistent quality. Such inconsistent quality includes fluctuations of size, frequency bandwidth, contact forces and resistance, etc. In the conventional probe contactors, another factor making the contact performance unreliable is a temperature change under which the probe contactors and the semiconductor wafer under test have different temperature expansion ratios. Thus, under the varying temperature, the contact positions therebetween vary which adversely affects the contact force, contact resistance and bandwidth.